SE-C-523690 discloses such a centrifugal separator, which is intended for cleaning of a gas containing liquid impurities in the form of oil particles and/or oil mist. The gas outlet for the cleaned gas extends in the known centrifugal separator from a lower part of the separation space. Immediately above the gas outlet, there is a shield element forming an annular surface extending into the separation space. Above the shield element at a distance therefrom, there is a number of outlet holes for discharge of the separated oil from the separation space. The separated oil is caught by the inner wall of the separation space and flows downwardly towards the outlet holes. Downstream the shield element, there is also an annular end surface in the proximity of the gas outlet.
The liquid impurities, for instance oil, which deposit on or are present in a layer close to such annular surfaces, will be conveyed radially inwardly towards the center of the separation space on the surface due to the fact that the rotation of the gas flow in this layer is decelerated by the friction against the non-rotating surface. It is therefore difficult to discharge the liquid impurities from the separation space.